1. Field of the Invention
The invention relates to an apparatus for the drying of tobacco materials comprising an endless conveying system for circulating a mixture of hot gases and steam entraining the tobacco materials.
Such drying apparatus, also known as stream or pneumatic dryers, are used in the preparation of tobacco, the pourable material to be dried being conveyed pneumatically with the aid of a stream of hot gas and steam through a pipe (the consumer apparatus) and in so doing dried. The material to be dried is introduced with special feed devices into the circulated hot gas and steam flow and, after drying, separated again from the stream of hot gas and steam.
The advantages of such a stream dryer reside in the simple construction, high output with a small base surface, and simultaneous pneumatic conveying of the material to be dried.
2. Description of the Prior Art
An apparatus, developed for the tobacco industry, for the drying of cut tobacco materials of the kind specified is known from German laid-open specification 2 841 874, and comprises an endless conveying line or system, namely a conduit system, for the circulating of a mixture of hot gas and steam, a device for feeding the material to be dried into the conveying system, a separator for the dried material, a heat source for the mixture of hot gas and steam in the conveying system, namely a heater, a control bypass bypassing the heat source and with an adjustable throughflow quantity for temperature regulation, and also a device for introducing steam into the conveying system.
This apparatus has the following disadvantage. Stream dryers of this kind are generally operated batchwise i.e. in the first instance a specific batch is put through, this being based on a precisely defined tobacco mixture. When the tobacco mixture is to be changed, which happens several times a day in some production plants, the entire dryer has to be shut off, and it cools down to an extent corresponding to the length of the pause in operations, so that a starting-up period is necessary each time. The cooling and the subsequent starting with heating-up to the operating temperature result in such stream dryers having a considerable energy consumption, and disturb the overall production runs (unnecessary delays due to having starting-up times).